1. Field of Invention
This invention relates to a process for the preparation of ethanol by the reaction of synthesis gas, i.e. a mixture of hydrogen and carbon monoxide, with methanol in the presence of an inert, oxygenated solvent using as a catalyst a combination of a cobalt-containing compound and a germanium-containing compound.
2. Prior Art
There is an increasing commercial potential for use of ethanol as a gasoline extender. As petroleum supplies are shifting, the synthesis gas technology area is gaining importance.
A great number of processes have been described in the art for reacting methanol with carbon monoxide and hydrogen in the presence of catalyst systems to produce ethanol. A general disadvantage of the art described processes is that they all produce a wide variety of other related products such as higher molecular weight alcohols, aldehydes, hydrocarbons, carboxylic acids, esters, etc. in addition to the desired ethanol.
In U.S. Pat. No. 3,285,948, for example, a method of forming alcohols is set out in which a cobalt catalyst system comprising cobalt carbonyl, a promoter and a ruthenium halide is described. Methanol homologation to ethanol has also been disclosed in U.S. Pat. Nos. 4,133,966, 4,239,924 and 4,239,925 wherein the three component catalyst systems consist of a cobalt-containing compound, a first promoter comprising an iodine compound and a second promoter comprising a ruthenium compound. Taylor, in U.S. Pat. No. 4,111,837, describes an improved process for converting methanol into ethanol and ethanol precursors using a cobalt carbonyl catalyst coupled with a novel heterogeneous cocatalyst system such as rhenium metal. Walker, in U.S. Pat. No. 4,277,634 and Riley et.al. in U.S. Pat. No. 3,248,432, teach the preparation of ethanol by the reaction of methanol, carbon monoxide, and hydrogen in the presence of a cobalt compound and an iodine promoter. Likewise in British Pat. No. 1,546,428 the preparation of ethanol is by reacting methanol with carbon monoxide and hydrogen in the presence of a solvent such as hydrocarbon solvent, a cobalt-containing catalyst such as cobalt iodide or bromide and a tertiary phosphine. Slinkard in U.S. Pat. No. 4,168,391 teaches a process for preparing ethanol by reaction of carbon monoxide, hydrogen and methanol in the presence of cobalt carbonyl and an oxygenated solvent such as dioxane.
All of the processes described above suffer from one or more disadvantages. In most cases the conversion of methanol is low, decomposition of the catalyst to insoluble and inactive species is observed, and a wide variety of products in addition to the desired ethanol are formed with consequent separation and disposal problems.